This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Protein kinases are a diverse set of regulatory enzymes responsible for signaling in a majority of metabolic pathways and cell behaviors. Kinases control signaling events within the cell through phosphorylation of substrate proteins. Identification of a given kinases'substrate proteins and their specific phosphorylation sites is essential to understanding kinases mediated signaling events. However, there is no general or trivial method for such identifications. We are investigating a method of elucidating kinase phosphorylation sites using small molecule inhibitors of a specific kinase, Nek2, as well as an inhibitor resistant mutant of Nek2 kinase. The method involves over-expressing the kinase of interest (Nek2) in human cells with an epitope tag that can be used to purify Nek2 and associated proteins from these cells. Mass Spec analysis can then be used to identify phosphorylation sites on these purified proteins. By making a quantitative comparison between samples treated with out Nek2 inhibitor and samples expressing the inhibitor resistant Nek2 mutant we can determine phosphorylation sites specifically linked to Nek2 kinase activity.